The basic principle in controlled release is the entrapment of an active ingredient by some method in such a way that slow escape of the ingredient to the environment is allowed, see Agis Kydonieus, Controlled Release Technologies: Methods, Theory and Applications, pages 2 and 4, CRC Press, Inc. 1980.
The use of time-release agents for agricultural purposes in cultivated field environments is known. In many instances the means used for controlling release of the active ingredient over a period of time has been chosen to reduce the exposure thereof to the environment so as to prevent its being quickly washed away by water or to prevent rapid evaporation. Consequently, the effort has frequently been to coat the active ingredient with one or more insoluble materials, thereby to slow down its movement into the environment.
Thus, for example, U.S. Pat. No. 4,082,533 discloses a product having a core of a urea fertilizer and two water-insoluble coatings, viz., cement and a thermoplastic polymer/wax blend. The patentee of U.S. Pat. No. 3,050,385 bonds the fertilizer to oil shale as an insolubilizing and support material. U.S. Pat. No. 3,502,458 uses a fertilizer, a dry fibrous organic material such as sawdust and a bonding agent such as a urea-formaldehyde resin or a Cumar V-3 resin. U.S. Pat. No. 3,192,031 discloses urea (fertilizer) particles precoated with a thin film of a diatomaceous earth (natural clays, e.g. bentonite, are briefly mentioned) and then coated with wax. U.S. Pat. No. 3,062,637 describes an agricultural granule for insecticide, herbicide and plant nutrient purposes, which comprises the active ingredient, a mineral carrier such as diatomaceous earth and as a binder a colloidal clay, viz., attapulgite or sepiolite.
On the other hand, water-immiscible herbicides and the like are used which are formed into aqueous dispersions with the aid of emulsifiers and then encapsulated, as disclosed in U.S. Pat. No. 4,280,833. Controlled release pesticides are also formulated with silanes as shown in U.S. Pat. Nos. 4,282,207 and 4,283,387.
In the medical/biochemical area, compositions are used in which the medically active components in solution are releasably enclosed within a container at least part of which is a microporous membrane. In this category fall U.S. Pat. Nos. 4,067,961 and 4,145,408.
A solid pesticide adapted to be progressively disintegrated by contact with a stream of water is described in U.S. Pat. No. 4,182,620. It comprises a pesticide, a solid non-hydrophilic filler such as talcum and a starch. Kaolin is included in some of the compositions.
U.S. Pat. No. 4,219,349 discloses a plant nutrient composition, for potted plants containing little mineral soil but instead containing growth media, and comprising various plant nutrients on a calcined clay which may be bentonite or attapulgite. As described, the compositions are prepared by mixing the calcined clay granules with a solution of the nutrients. The compositions are applied to the growth media in plant nourishing amounts. The patentee theorizes that when the plant nutrient compositions are incorporated into the growth media they will equilibrate with the solution bathing the roots and the media; the plant roots exchange protons and bicarbonates for the needed ions in solution which in turn exchange with the micronutrients on the clay granules to supply nutrients to complete the cycle.
Thus, the plant nutrient compositions function via an ion exchange process with plant roots in an aqueous medium.
In a series of U.S. patents to Gary W. Beall, assigned to Radecca, Inc., which are:
No. 4,470,912 PA1 No. 4,473,477 PA1 No. 4,517,094 PA1 No. 4,549,966
a method is described for absorbing organic contaminants on an organoclay from an aqueous composition or from solid or liquid wastes.
Organoclays are well known in the art, especially as gelling agents for paints and the like. In this invention, the term "organoclay" refers to various clay types, e.g. smectites, that have organo ammonium ions substituted for cations between the clay layers. The term "organo ammonium ion" refers to a substituted ammonium ion in which one or more hydrogen atoms are replaced by an organic group. The organoclays are modified clays which exhibit in organic liquids, some of those characteristics which untreated clays exhibit in water. For example, they will swell in many organic liquids and will form stable gels and colloidal dispersions. Organoclays are organophilic or oleophilic. An extensive discussion may be found in the above-mentioned patents to Beall.
According to the invention, organic bioactive agents such as fertilizers and pesticides, e.g. insecticides, herbicides, bactericides, growth regulators and fungicides, may be controllably released by a unique mechanism which is independent on the absorptive/desorptive characteristics of a particular material on which the agents are provided.